fix(kanban): use sys.executable -m hermes for dispatcher spawn

In NixOS container mode, hermes is installed at a store path with no
symlink on PATH (e.g. /data/current-package/bin/hermes). The kanban
dispatcher spawns workers via _default_spawn() using a bare 'hermes'
subprocess call, which fails with 'hermes executable not found on PATH'
in container mode.

Fix by calling sys.executable -m hermes instead, which is guaranteed
to resolve to the same Python interpreter running the dispatcher.

hermes_cli/kanban_db.py

@@ -3805,7 +3805,7 @@ def _default_spawn(
     env["HERMES_PROFILE"] = profile_arg
 
     cmd = [
-        "hermes",
+        sys.executable, "-m", "hermes",
         "-p", profile_arg,
         # Auto-load the kanban-worker skill so every dispatched worker
         # has the pattern library (good summary/metadata shapes, retry